Odds Conversion

Odds conversion is the process of translating a betting price between the three main formats — American (moneyline), decimal and fractional — and into its implied probability, without changing the price's underlying value. The same edge is expressed differently by each format, so converting lets you compare prices across sportsbooks and regions on a like-for-like basis. The formulas are straightforward. Decimal odds equal fractional odds plus 1 (so 2/1 becomes 3.00). Implied probability from decimal odds is 1 divided by the decimal price, expressed as a percentage. Positive American odds convert to decimal as (odds/100) + 1, while negative American odds convert as (100/|odds|) + 1. Reverse the arithmetic to go back the other way. Worked example: a price of +150 in American format means you win 150 units on a 100-unit stake. Convert it to decimal: (150/100) + 1 = 2.50. As a fraction that is 3/2. The implied probability is 1/2.50 = 0.40, or 40%. A 20 dollar stake at 2.50 returns 50 dollars total (20 x 2.50), a 30 dollar profit. Every one of those expressions describes the identical bet — only the notation differs. For a bettor, fluency in conversion is practical rather than academic: it exposes which book offers the best price and reveals the bookmaker's margin once you sum the implied probabilities across a market and see they exceed 100%. That excess is the overround. Comparing implied probability against your own estimate is also the basis of spotting value. Compare with implied probability, decimal odds, american odds, fractional odds and overround.